The present invention relates to a fifth wheel and more particularly, relates to a fifth wheel structure having a rotatable bearing plate.
As is well known in the art, tractor trailers use a coupling known as a fifth wheel wherein the trailer has one portion of the coupling and the truck or tractor unit has a further portion of the fifth wheel. Conventionally, the fifth wheel construction for the truck unit comprises a substantially round flat plate to form a tractor bearing surface. The semi trailer also includes a plate member with a king pin extending downwardly to locate and seat within a slot within the fifth wheel portion mounted on the truck unit. There are provided means for locking the kingpin in place when the truck is put into position with the two portions of the fifth wheel engaging together.
It is also well known in the art that friction between the two bearing surfaces develops and this can lead to many problems including driver fatigue, increased tire wear, poor handling, and structural problems associated with the units.
In order to minimize the above problems, it is also well known to place a lubricant between the two bearing surfaces. This lubricant, which is usually grease, helps but has not been found to be the solution since it is necessary to frequently replenish the grease and it is also dirty and messy. Moreover, the lubricant can be squeezed out of place and in cold weather, the lubricant can stiffen. This can again lead to handling and performance problems and cause dangerous vehicle handling characteristics.
In order to overcome the above problems, there have been proposals in the art to utilize substrates having a low co-efficient of friction. This solution does suffer, however, from the fact that dirt can enter these units and still lead to handling problems.
It has also been suggested that a rotating structure may be utilized in order to minimize the friction. While such structures have been proposed, generally they have not been practical as many have been relatively complex, expensive, heavy and difficult to maintain.